1. Field of the Invention
The present invention relates to a passage detection apparatus of an object that can detect a passage of an object in a specific space.
2. Description of the Related Art
For example, various methods of manufacturing a so-called DNA chip (a DNA micro array) are well known. The DNA chip is generally constructed by arraying and fixing micro spots of several thousand to ten thousand or more kinds of different DNA pieces on a substrate, such as microscope slide glass, with high density.
As examples of the DNA chip manufacturing methods, there have been proposed methods of manufacturing a DNA chip using a micropipette for ejecting drops having micro volume (for example, see the following Patent References 1 and 2). The micropipette includes an injection port for injecting a sample solution from the outside, a cavity for allowing the sample solution injected from the injection port to be filled therein, an ejection port communicating with the cavity, and a piezoelectric/electrostrictive element constructed to change the interior volume of the cavity such that the sample solution can be ejected from the ejection port.
According to the above-described DNA chip manufacturing methods, the interior volume of the cavity is changed by the driving operation of the piezoelectric/electrostrictive element. As the interior volume of the cavity is changed, the sample solution moves from the cavity to the ejection port in the form of a streamline flow. That is, a predetermined amount of the sample solution is delivered from the cavity to the ejection port. As the predetermined amount of the sample solution is ejected from the ejection port, micro drops of the sample solution are generated. The micro drops of the sample solution ejected from the micropipette are attached to the substrate, and the micro drops are arrayed and fixed on the substrate as micro spots. In this way, the DNA chip is manufactured.
An apparatus constructed to eject a micro object (hereinafter, simply referred to as a “micro object ejection apparatus”), such as the micropipette used in the DNA chip manufacturing method as described above, may be utilized in various technical fields.
[Patent Reference 1] Japanese Unexamined Patent Publication No. 2001-124789
[Patent Reference 2] Japanese Unexamined Patent Publication No. 2001-186881
The micro object ejection apparatus of this type has been required to more correctly detect the passage of the object having more micro size. This can be achieved by enhancing an S/N ratio in the detection of a passage of an object.